Fabrication of Al-3.7?Pct Si-0.18?Pct Mg Foam Strengthened by AlN Particle Dispersion and its Compressive Properties

Al-3.7 pct Si-0.18 pct Mg foams strengthened by AlN particle dispersion were prepared by a melt foaming method, and the effect of foaming temperature on the foaming behavior was investigated. Al-3.7 pct Si-0.18 pct Mg alloy containing AlN particles was prepared by noncompressive infiltration of Al powder compacts with molten Al alloy in nitrogen atmosphere, and it was foamed at different foaming temperatures ranging from 1023 to 1173 K. The porosity of prepared foam decreases and the pore structure becomes homogeneous with increasing foaming temperature. When the foaming temperature is higher than 1123 K, homogeneous pores are formed in the prepared ingot without using oxide particles and metallic calcium granules, which are usually used for stabilizing a foaming process. This stabilization of the foaming at high temperatures is possibly caused by Al₃Ti intermetallic compounds formed at high temperature and AlN particles. Compression tests for the prepared foams revealed that the absorbed energy per unit mass of prepared Al-3.7 pct Si-0.18 pct Mg foam is higher than those of aluminum foams strengthened by alloying or dispersion of reinforcements. It is remarkable that the oscillation in stress, which usually appears in strengthened aluminum foams, does not appear in the plateau stress region of the present Al-3.7 pct Si-0.18 pct Mg foam. The homogeneity in cell walls and pore morphology due to the stabilization of pore formation and growth by AlN and Al₃Ti particles is a possible cause of this smooth plateau stress region.     

Effect of Partial Substitution of Mn for Ni on Mechanical Properties of Friction Stir Processed Hypoeutectic Al-Ni Alloys

In this study, the mechanical properties of as-cast and FSPed Al-2Ni-xMn alloys (x?=?1, 2, and 4 wt pct) were investigated and compared with those of the as-cast and FSPed Al-4Ni alloy. According to the results, the substitution of 2 wt pct Mn for 2 wt pct Ni leads to the formation of fine Mn-rich intermetallics in the microstructure increasing the tensile strength, microhardness, fracture toughness, and specific strength of alloy by 22, 56, 45, and 35 pct, respectively. At higher Mn concentrations, the formation of large Mn-rich platelets in the microstructure reduces the tensile properties. Friction stir processing at 12 mm/min and 1600 rpm significantly enhances both the strength and ductility of the alloy. The tensile strength, yield strength, fracture strain, fracture toughness, microhardness, and specific strength of FSPed Al-2Ni-4Mn alloy improved by 97, 83, 30, 380, 152, and 110  pct, respectively, as compared to those of the as-cast Al-4Ni alloy. This can be attributed to dispersion strengthening of Ni- and Mn-rich dispersoids, formation of ultrafine grains, and elimination of casting defects. The fractography results also show that the brittle fracture mode of the as-cast Mn-rich alloys turns to a more ductile mode, comprising fine and equiaxed dimples in FSPed samples.     

Effect of Multi-Scale Thermoelectric Magnetic Convection on Solidification Microstructure in Directionally Solidified Al-Si Alloys Under a Transverse Magnetic Field

The influence of a transverse magnetic field (B < 1 T) on the solidification structure in directionally solidified Al-Si alloys was investigated. Experimental results indicate that the magnetic field caused macrosegregation, dendrite refinement, and a decrease in the length of the mushy zone in both Al-7 wt pct Si alloy and Al-7 wt pct Si-1 wt pct Fe alloys. Moreover, the application of the magnetic field is capable of separating the Fe-rich intermetallic phases from Al-7 wt pct Si-1 wt pct Fe alloy. Thermoelectric magnetic convection (TEMC) was numerically simulated during the directional solidification of Al-Si alloys. The results reveal that the TEMC increases to a maximum ( \( u_{\rm{max} } \) ) when the magnetic field reaches a critical magnetic field strength ( \( B_{\rm{max} } \) ), and then decreases as the magnetic field strength increases further. The TEMC exhibits the multi-scales effects: the \( u_{\rm{max} } \) and \( B_{\rm{max} } \) values are different at various scales, with \( u_{\rm{max} } \) decreasing and \( B_{\rm{max} } \) increasing as the scale decreases. The modification of the solidification structure under the magnetic field should be attributed to the TEMC on the sample and dendrite scales.     

Study on Microstructures of Al-4 wt pct V Master Alloys

Aluminum (Al)-V master alloys have attracted attention, because they can potentially be efficient grain refiners for wrought aluminum alloys. In this paper, the microstructure and factors affecting the microstructure of Al-4 wt pct V master alloys were investigated by means of controlled melting and casting processes followed by structure examination. The results showed that the type and morphology of the V-containing phases in Al-V master alloys were strongly affected by the temperature of the melt, concentration of vanadium in solution in the melt and the cooling conditions. Two main V-containing phases, Al₃V and Al₁₀V, which have different shapes, were found in the alloys prepared by rapid solidification. The Al₃V phase formed when there were both a high temperature (1273 K to 1673 K (1000 °C to 1400 °C)) and a relatively high vanadium content of 3 to 4 wt pct, while the Al₁₀V phase formed at a low temperature (<1373 K (1100 °C)) or a low vanadium content in the range of 1 to 3 wt pct. The results also showed that the type of V-containing phase that formed in the Al-4 wt pct V master alloy was determined by the instantaneous vanadium content.     

Solidification of Al-4.5 wt pct Cu-Replicated Foams

Microcellular Al-4.5 wt pct Cu of 400- or 75-μm average pore diameter is solidified at cooling rates ranging from ?30 K/min to ?0.45 K/min (?30 °C/min to ?0.45 °C/min). In the 400-μm pore size samples, the dendritic character is lost, and the level of microsegregation, which is quantified by the minimum copper content of the matrix, is reduced when the cooling rate is lowered. The 75-μm pore size samples show no dendritic microstructural features and low levels of microsegregation, even at the higher cooling rates explored. Microstructural maps, based on solidification theory developed for metal matrix composites, satisfactorily describe the microstructure of the Al-4.5 wt pct Cu foams. A finite difference model giving the minimum copper content as a function of the reinforcement size and cooling rate, developed for fiber-reinforced metals, is also valid for replicated Al-4.5 wt pct Cu foam. This work thus extends to particulate composites and, by extension, to replicated microcellular alloys, results originally derived from the study of fiber-reinforced metal solidification.     

A Study of the Effect of Nanosized Particles on Transient Liquid Phase Diffusion Bonding Al6061 Metal–Matrix Composite (MMC) Using Ni/Al2O3 Nanocomposite Interlayer

Transient liquid phase (TLP) diffusion bonding of Al-6061 containing 15 vol pct alumina particles was carried out at 873 K (600 °C) using electrodeposited nanocomposite coatings as the interlayer. Joint formation was attributed to the solid-state diffusion of Ni into the Al-6061 alloy followed by eutectic formation and isothermal solidification of the joint region. An examination of the joint region using an electron probe microanalyzer (EPMA), transmission electron microscopy (TEM), wavelength-dispersive spectroscopy (WDS), and X-ray diffraction (XRD) showed the formation of intermetallic phases such as Al₃Ni, Al₉FeNi, and Ni₃Si within the joint zone. The result indicated that the incorporation of 50 nm Al₂O₃ dispersions into the interlayer can be used to improve the joint significantly.     

Diffusion Brazing of Al6061/15 Vol. Pct Al2O3p Using a Cu-Sn Interlayer

Diffusion brazing of Al-6061 alloy containing 15 vol. pct Al₂O₃ particles was attempted using Cu-Sn interlayer. Joint formation was attributed to the solid-state interdiffusion of Cu and Sn followed by eutectic formation and subsequent isothermal solidification. Examination of the joint region using scanning electron microprobe analyzer (EPMA), wavelength dispersive spectroscopy (WDS) and X-ray diffraction (XRD) showed the formation of intermetallic phases such as Al₇Cu₃Mg₃, Mg₂Cu₆Al₅, Cu₃Sn, and Mg₂Sn. The results indicated an increase in joint strength with increasing bonding time giving the highest joint shear strength of 94 MPa at a bonding duration of 3 hours.     

A Novel Characterization Technique to Determine Pore Susceptibility of Alloying Elements in Aluminum Alloys

An investigation into the effect of ternary alloying element additions such as copper, magnesium, manganese, zinc, and nickel on pore formation in cast Al-12.6-wt pct Si eutectic alloy by employing a novel pore characterization technique is reported here. In this approach, the low-pressure testing method was combined with the metal foam manufacturing technique of intentionally adding TiH₂, which enhances hydrogen pore formation and offers a method to distinguish the effect of individual alloying elements on hydrogen porosity formation.     

Microstructures and Tensile Properties of Hot-Extruded Al Matrix Composites Containing Different Amounts of Al4Sr

In this investigation, the effect of hot extrusion process has been studied on the microstructure and tensile properties of aluminum matrix composite containing different amounts (10, 15, and 20 wt pct) of Al₄Sr intermetallic phase. Microstructural examinations assessed by scanning electron microscopy revealed that hot extrusion breaks large Al₄Sr particles and reduces their length tremendously. It was also found that although the addition of Al₄Sr content in the composite reduces ultimate tensile strength and elongation values, hot extrusion improves tensile results significantly. Remarkable result of this study was concerned with significant improvement in the toughness of hot-extruded Al-10 wt pct Al₄Sr composite in which elongation values raised up to 22 pct. Therefore, optimum amount of Al₄Sr intermetallic in the composite was found to be 10 wt pct. Fractographic examinations revealed that hot extrusion encourages ductile mode of fracture by introducing homogeneous distribution of fine dimples on the fracture surface of the composites.     

Effects of Copper and Austempering on Corrosion Behavior of Ductile Iron in 3.5 Pct Sodium Chloride

Although alloying and heat treatments are common industrial practices to obtain ductile irons with desired mechanical properties, related information on how the two practices affect corrosion behavior is scarce. In this study, two ductile irons—with and without 1 wt pct copper addition—were austempered to obtain austempered ductile irons (ADIs). Polarization tests and salt spray tests were conducted to explore how both copper-alloying and austempering heat treatments influenced the corrosion behavior of ductile irons. The results showed that the corrosion resistance of 1 wt pct copper-alloyed ductile iron was better than that of the unalloyed one, while ADI had improved corrosion resistance compared with the as-cast. In particular, the ductile iron combined with the copper-alloying and austempering treatments increased the corrosion inhibition efficiency up to 84 pct as tested in 3.5 wt pct NaCl solution.     

Two-Zone Microstructures in Al-18Si Alloy Powders

Hypereutectic Al-18 wt pct Si alloy is widely used in automotive industry as a wear-resistant alloy for engine components. However, in the last few years, this traditional composition is being considered for processing by different rapid solidification methods. Positive points include its low thermal expansion and uniform distribution of surface oxides. Nevertheless, the microstructural aspects of Al-Si powders of 18 wt pct Si are still need to be addressed, such as, the eutectic Si morphology, size, and distribution generated by different process conditions during rapid solidification. Based on a detailed quantitative analysis of the microstructures of rapid solidified Al-18 wt pct Si in this work, solidification conditions that yield specific Si morphologies, Si spacing, and thermal cooling conditions are outlined. The focus is determining the solidification conditions that will yield a specified shape of eutectic Si. It is shown that Si morphology is dependent on a combination of growth velocity (based on modified JH model) and temperature gradient. Furthermore, the highest hardness is achieved with globular morphologies of Si. The processing conditions required to achieve these properties are outlined.     

The Development of the Low-Cost Titanium Alloy Containing Cr and Mn Alloying Elements

The α + β-type Ti-4.5Al-6.9Cr-2.3Mn alloy has been theoretically designed on the basis of assessment of the Ti-Al-Cr-Mn thermodynamic system and the relationship between the molybdenum equivalent and mechanical properties of titanium alloys. The alloy is successfully prepared by the split water-cooled copper crucible, and its microstructures and mechanical properties at room temperature are investigated using the OM, SEM, and the universal testing machine. The results show that the Ti-4.5Al-6.9Cr-2.3Mn alloy is an α + β-type alloy which is consistent with the expectation, and its fracture strength, yield strength, and elongation reach 1191.3, 928.4 MPa, and 10.7 pct, respectively. Although there is no strong segregation of alloying elements under the condition of as-cast, the segregation of Cr and Mn is obvious at the grain boundary after thermomechanical treatment.     

Coating of 6028 Aluminum Alloy Using Aluminum Piston Alloy and Al-Si Alloy-Based Nanocomposites Produced by the Addition of Al-Ti5-B1 to the Matrix Melt

The Al-12 pctSi alloy and aluminum-based composites reinforced with TiB₂ and Al₃Ti intermetallics exhibit good wear resistance, strength-to-weight ratio, and strength-to-cost ratio when compared to equivalent other commercial Al alloys, which make them good candidates as coating materials. In this study, structural AA 6028 alloy is used as the base material. Four different coating materials were used. The first one is Al-Si alloy that has Si content near eutectic composition. The second, third, and fourth ones are Al-6 pctSi-based reinforced with TiB₂ and Al₃Ti nano-particles produced by addition of Al-Ti5-B1 master alloy with different weight percentages (1, 2, and 3 pct). The coating treatment was carried out with the aid of GTAW process. The microstructures of the base and coated materials were investigated using optical microscope and scanning electron microscope equipped with EDX analyzer. Microhardness of the base material and the coated layer were evaluated using a microhardness tester. GTAW process results in almost sound coated layer on 6028 aluminum alloy with the used four coating materials. The coating materials of Al-12 pct Si alloy resulted in very fine dendritic Al-Si eutectic structure. The interface between the coated layer and the base metal was very clean. The coated layer was almost free from porosities or other defects. The coating materials of Al-6 pct Si-based mixed with Al-Ti5-B1 master alloy with different percentages (1, 2, and 3 pct), results in coated layer consisted of matrix of fine dendrite eutectic morphology structure inside α-Al grains. Many fine in situ TiAl₃ and TiB₂ intermetallics were precipitated almost at the grain boundary of α-Al grains. The amounts of these precipitates are increased by increasing the addition of Al-Ti5-B1 master alloy. The surface hardness of the 6028 aluminum alloy base metal was improved with the entire four used surface coating materials. The improvement reached to about 85 pct by the first type of coating material (Al-12 pctSi alloy), while it reached to 77, 83, and 89 pct by the coating materials of Al-6 pct Si-based mixed with Al-Ti5-B1 master alloy with different percentages 1, 2, and 3 pct, respectively.     

On the Optimization of Compressibility and Hardenability of Sinter-Hardenable PM Steels

Sinter-hardenable steel powders eliminate the extra steps normally required for heat treating since they allow for direct quenching of components at the end of the sintering cycle with a forced convection cooling unit. The current article presents the results of the effect of the alloying method on the optimization of compressibility and sinter-hardenability of sinter-hardenable PM steels. Water-atomized steel powders were produced. Two successive designs of experiments were used to optimize the chemical composition with prealloyed (nickel, chromium, molybdenum, and manganese) and admixed elements (nickel, chromium, manganese, and copper). Static mechanical properties were also characterized. Results show that among all of the combinations of chemical elements and within the range of concentrations studied, the optimum sinter-hardenable powder had the following prealloyed chemistry: 1.5 wt pct Ni, 1 to 1.25 wt pct Mo, and 0.40 to 0.55 wt pct Cr.     

Evolution of Intermetallics,Dispersoids, and Elevated Temperature Properties at Various Fe Contents in Al-Mn-Mg 3004 Alloys

Nowadays, great interests are rising on aluminum alloys for the applications at elevated temperature, driven by the automotive and aerospace industries requiring high strength, light weight, and low-cost engineering materials. As one of the most promising candidates, Al-Mn-Mg 3004 alloys have been found to possess considerably high mechanical properties and creep resistance at elevated temperature resulted from the precipitation of a large number of thermally stable dispersoids during heat treatment. In present work, the effect of Fe contents on the evolution of microstructure as well as high-temperature properties of 3004 alloys has been investigated. Results show that the dominant intermetallic changes from α-Al(MnFe)Si at 0.1 wt pct Fe to Al₆(MnFe) at both 0.3 and 0.6 wt pct Fe. In the Fe range of 0.1–0.6 wt pct studied, a significant improvement on mechanical properties at elevated temperature has been observed due to the precipitation of dispersoids, and the best combination of yield strength and creep resistance at 573 K (300 °C) is obtained in the 0.3 wt pct Fe alloy with the finest size and highest volume fraction of dispersoids. The superior properties obtained at 573 K (300 °C) make 3004 alloys more promising for high-temperature applications. The relationship between the Fe content and the dispersoid precipitation as well as the materials properties has been discussed.     

Co Effect on As-cast and Heat-Treated Microstructures in Ru-Containing Single-Crystal Superalloys

The effect of Co on the as-cast and heat-treated microstructures was investigated in two experimental Ni-based single-crystal superalloys containing low levels of Re and Ru. The experimental results indicated that increasing the Co content from 7.9 to 15.8 wt pct decreased the volume fraction of (γ + γ′) eutectic and the solidification segregation ratio of W. High levels of Co additions were also found to decrease the solvus temperatures of the γ′ phase and (γ + γ′) eutectic as well as the solidus temperature. During the long-term thermal exposure at 1373 K (1100 °C), no TCP phases precipitated in either alloy. However, the coarsening and coalescence of γ′ precipitates in the alloy containing 15.8 wt pct Co was slower than that in the other alloy with 7.9 wt pct Co. In the current study, high levels of Co additions decreased the equilibrium volume fraction of γ′ phase, leading to a change in the partitioning ratios of TCP-forming elements Cr, Mo, Re, and W between the γ and γ′ phases. This change resulted in a lower degree of elemental supersaturation in the γ matrix and improved the phase stability of the γ/γ′ microstructure. These experimental results were then compared with those obtained from multi-component thermodynamic calculations, and good agreement was observed.     

Recycling of Magnesium Alloy Employing Refining and Solid Oxide Membrane (SOM) Electrolysis

Pure magnesium was recycled from partially oxidized 50.5 wt pct Mg-Al scrap alloy and AZ91 Mg alloy (9 wt pct Al, 1 wt pct Zn). Refining experiments were performed using a eutectic mixture of MgF₂-CaF₂ molten salt (flux). During the experiments, potentiodynamic scans were performed to determine the electrorefining potentials for magnesium dissolution and magnesium bubble nucleation in the flux. The measured electrorefining potential for magnesium bubble nucleation increased over time as the magnesium content inside the magnesium alloy decreased. Potentiostatic holds and electrochemical impedance spectroscopy were employed to measure the electronic and ionic resistances of the flux. The electronic resistivity of the flux varied inversely with the magnesium solubility. Up to 100 pct of the magnesium was refined from the Mg-Al scrap alloy by dissolving magnesium and its oxide into the flux followed by argon-assisted evaporation of dissolved magnesium and subsequently condensing the magnesium vapor. Solid oxide membrane electrolysis was also employed in the system to enable additional magnesium recovery from magnesium oxide in the partially oxidized Mg-Al scrap. In an experiment employing AZ91 Mg alloy, only the refining step was carried out. The calculated refining yield of magnesium from the AZ91 alloy was near 100 pct.     

Control of the Mechanical Asymmetry in an Extruded MN11 Alloy by Static Annealing

An extruded Mg-1 wt pct Mn-1 wt pct Nd (MN11) alloy with a recrystallized microstructure and a weak texture was subjected to different thermal treatments at temperatures ranging from 548 K to 673 K (275 °C to 400 °C) for time intervals between 1 and 45 hours. Room-temperature mechanical tests were carried out in tension and compression at 10^?3 s^?1 in order to investigate the effect of annealing on the mechanical behavior. Microstructural examinations revealed that both the annealing temperature and time have little effect on the grain size and on the texture, which are mainly controlled by the presence of thermally stable Mn-containing particles and by the segregation of Nd to the grain boundaries. However, the composition and distribution of the Nd-containing particles vary significantly for the different annealing conditions. The annealed bars exhibit a subtle change in the tensile and compressive yield stress relative to the as-extruded bar and a somewhat larger mechanical asymmetry. The present results suggest that the Nd-containing phases, as well as Nd solute atoms, play a significant role in the mechanical behavior of the MN11 alloy by changing the relative critical resolved shear stress of the different deformation modes.     

Effect of Continuous Galvanizing Heat Treatments on the Microstructure and Mechanical Properties of High Al-Low Si Transformation Induced Plasticity Steels

Heat treatments were performed using an isothermal bainitic transformation (IBT) temperature compatible with continuous hot-dip galvanizing on two high Al–low Si transformation induced plasticity (TRIP)-assisted steels. Both steels had 0.2 wt pct C and 1.5 wt pct Mn; one had 1.5 wt pct Al and the other had 1 wt pct Al and 0.5 wt pct Si. Two different intercritical annealing (IA) temperatures were used, resulting in intercritical microstructures of 50 pct ferrite (α)-50 pct austenite (γ) and 65 pct α-35 pct γ. Using the IBT temperature of 465 °C, five IBT times were tested: 4, 30, 60, 90, and 120 seconds. Increasing the IBT time resulted in a decrease in the ultimate tensile strength (UTS) and an increase in the uniform elongation, yield strength, and yield point elongation. The uniform elongation was higher when using the 50 pct α-50 pct γ IA temperature when compared to the 65 pct α-35 pct γ IA temperature. The best combinations of strength and ductility and their corresponding heat treatments were as follows: a tensile strength of 895 MPa and uniform elongation of 0.26 for the 1.5 pct Al TRIP steel at the 50 pct γ IA temperature and 90-second IBT time; a tensile strength of 880 MPa and uniform elongation of 0.27 for the 1.5 pct Al TRIP steel at the 50 pct γ IA temperature and 120-second IBT time; and a tensile strength of 1009 MPa and uniform elongation of 0.22 for the 1 pct Al-0.5 pct Si TRIP steel at the 50 pct γ IA temperature and 120-second IBT time.     

Metastable β-type Ti-30Nb-1Mo-4Sn Alloy with Ultralow Young’s Modulus and High Strength

The effect of thermo-mechanical treatment on the mechanical properties of a novel metastable β-type Ti-30Nb-1Mo-4Sn (wt pct) alloy has been investigated. The solution-treated alloy consists of β and α″ phases and exhibits a two-stage yielding with a low yield stress (around 100 MPa). After cold rolling at a reduction of 87.5 pct and subsequent annealing treat at 623 K (350 °C) for 30 minutes, a fine microstructure with nano-sized α precipitates distributed in small β grains as well as high density of dislocations was obtained to achieve a yield strength of 954 MPa and an ultimate tensile strength of 999 MPa. With low stability of β phase and small volume fraction of α precipitates, the annealed specimen exhibits a low Young’s modulus of 45 GPa. Such an excellent combination of the low elastic modulus and high strength in mechanical properties indicates a great potential candidate for biomedical applications.